1. Field of the Invention
This invention relates to a semiconductor device and its manufacturing method especially suitable for application to semiconductor lasers, light emitting diodes or electron mobility devices using nitride III-V compound semiconductors.
2. Description of the Related Art
GaN semiconductors are direct transition semiconductors having forbidden band widths ranging from 1.9 eV to 6.2 eV and enabling realization of light emitting devices capable of emitting light over a wide range from the visible region to the ultraviolet region. For these properties, they have become of interest recently, and are placed under active developments. Additionally, GaN semiconductors have a large possibility as material of electron transport devices. Saturation electron velocity of GaN is approximately 2.5.times.10.sup.7 cm/s, which is larger than those of GaAs and SiC, and its breakdown electric field is as large as approximately 5.times.10.sup.6 V/cm next to the intensity of diamond. For these reasons, GaN semiconductors have been expected to be greatly hopeful as materials of electron transport devices for high frequencies, high temperatures and high power.
There is a semiconductor laser called LOP (laser on photo diode) in which a laser chip is mounted on a sub mount having formed a photo diode for monitoring light output. LOP is packaged in the following manner.
As shown in FIG. 1A, first made is a Sn solder layer (not shown) on a surface of a Si substrate 101 having formed light output monitoring photo diodes (not shown) in individual pellets by vacuum evaporation, for example. Next, as shown in FIG. 1B, the Si substrate 101 is half-cut between individual pellets by dicing. Next, as shown in FIG. 1C, separately prepared laser chips 102 are mounted on respective pellets on the Si substrate 101 in a predetermined positional relation therewith. After that, by heating the Si substrate 101, the Sn solder layer formed thereon is welded to the bottom surface of the laser chips 102. Then, after the Si substrate 101 is fully cut between respective pellets, here again by dicing, it is pulled and broken into chips. As a result, a LOP chip 103 as shown in FIG. 1D is obtained. The LOP chip 103 is thereafter mounted on a heat sink of a package, not shown. Further, a cap with a window is applied onto the package to seal it. Thus, assembling is completed.
The conventional method of semiconductor lasers explained above was certainly more rationalized than methods relying on individually welding each laser chip. However, it was not a so-called batch process, but still needed a number of steps for assembling. Therefore, its productivity was not satisfactory. This problem also lies when manufacturing a semiconductor laser using GaN semiconductors.